"Don't write games in Rust" and how fast and easy can you access mutable data?

I've listened to Better Software conference, and once again heard people say "don't use Rust, it slows you down, you have to fight with it." I guess part of it comes from the fact that in C you can both keep references to structures, and mutate them, which is impossible in Rust. I haven't done game development, and wonder where you need these references to mutated data? In Rust, the obvious solution is, to use vector/array indices instead of refs. Accessing vector or array by index generates r...